Process for treatment of metals



Reiuued Mar. 30, 1943 PROCESS FOR- TBEATMENT F METALS Robert W.Shoemaker, Anderson, Ind'., assignor to Agnes J. Reeves Greer,Morgantown, W. Va.

No Drawinr Original No. 2,257,133, dated September 30, 1941, Serial No.279,053, June 14,

1942, Serial No. 459,037

13 Claims. (Cl. 117-49) The invention relates to the treatment of metal,particularly to the cleaning of metal articles as by pickling. and ismore especially concerned with a process designed to more effectivelyneutralize the acid and clean the metal to prevent corrosion of themetal after the pickling operation and prior to the cold rolling orother processing thereof.

Corrosion is an oxidation process, favored by the presenc of air andmoisture, especially in the presence of hydrogen ions, which means freeacid.

The problem, therefore, is to remove these substances from the surfacesof the metal and to prevent their gaining access thereto before the coldrolling or other processing of the metal is performed.

It is common practice in the pickling of metal articles to immerse themin'an acid solution for a sumcient time to remove the products ofoxidation from the surfaces of the metal and to then rinse the articlesin cold water, followed by a hot water or alkaline rinse in an effort toremove the acid therefrom.

Even if the articles are to be immediately subiected to a furtherprocessing such as cold rolling, they are sometimes oiled to preventthem from rusting, but it often happens that the metal mats in a shorttime even when treated in this manner.

It was commonly believed that this rust was caused by the exposure ofthe wet metal to the air before the surfaces thereof were oiled, and itis known that attempts have been made to prevent this condition byapplying oil to the surface of the metal while it is still wet from therlnsingoperation.

It has been found by experience, however, that the application of oil tothe surface of the metal. particularly strip steel before the same iscold rolled, is obiectionable as the oil produces a black scum upon thesteel and the cold rolls through which the strips are passed, as well asupon the back-up rolls therefor.

It has also been found that metal treated in this manner frequentlyrusts regardless of the manner in which the oil is applied to thesurface thereof, and this is believed to be due to the fact that thepickling acid is not entirely removed from the surfaces and pores of themetal since this free acid or hydrogen ions remaining upon the surfaceor in the pores of the metal will cause oxidation when the metal isexposed to air and moisture.

Application for reissue September 19,

discovery that metal articles can be prevented from rusting after thepickling operation by virtually removing all traces of acid from thesurfaces and pores of the metal and immediately treating the surfaces ofthe metal to prevent the oxygen of the air from gaining access thereto.

The improved method may be carried out in the three conventional tanks,the pickling operation being performed in th first tank, theneutralizing and cleansing operation in the second tank, and the coatingfor preventing oxidation is applied in the third tank.

Another important object of the invention is to eliminate the use of oilupon the surfaces of the pickled and cleaned metal so as to prevent theformation of a black scum upon the steel and the cold rolls throughwhich the metal may be later passed; and to coat the surfaces of themetal with an ester or one or both of its resulting saponificationproducts, which may be either a polyhydric alcohol such as glycerine,glycol, or a soluble ammonium soap such as ammonium oleate, ammoniumlinoleate or ammonium laurate.

A further object is to provide for thoroughly cleaning the surfaces andpores of the metal to virtually remove all traces of acid therefrom bymeans of caustic alkali and a wetting agent.

In treating coils of metal the invention has been carried out in apickling machine such as disclosed in Greer Patent No. 2,091,921,wherein the coils are suspended upon mandrels and rotated as they aremoved forward through the pickling and washing baths.

The coils are first passed through the acid tank which containsapproximately 6% sulphuric acid in water at a temperature of between andF. together with a suitable inhibitor.

After the coils are pickled in the acid tank they are transferred to thefirst washing tank in which the water may be maintained at a temperaturebetween 180 and 212' 1'.

Hot water is used in this tank instead of the usual cold waterordinarily used for the first rinse, as it is found that hot water morethoroughly cleanses the metal.

In order to completely remove all of the acid from the metal ordinarysoap,caustic alkali, and a wetting agent are added to the hot water.

Only a relatively small quantity of each of these ingredients isnecessary to give very satisfactory results. Ordinary soap powder orsoap chips may be used in proportions ranging between .125% to 275%. Inactual practice with a tank containing approximately 5600 gallons ofwater, 10 to 20 pounds of ordinary soap powder or soap chips gave verysatisfactory results, the soap powder or soap chips used being soldunder the name of Ozonite. Any ordinary soap powder or soap chips whichare eifective in alkaline solution may be used for the purpose.

The ordinary soap is used for the purpose of cleansing the metal, aswell as lubricating the mandrel and coil when the process is carried outin a machine in which the coils are rotated upon mandrels as in themanner generally shown in the Greer patents; and as above pointed cut,oil is not a suitable lubricant since it leaves a black scum upon themetal coils.

The caustic alkali used may be either caustic soda or a preparedneutralizing compound such as super alkali No. 4 which is a mixture ofsodium carbonate and sodium hydroxide, and may be in an amount rangingfrom 275% to 550%.

From 50 to '150 pounds of caustic soda in this tank have given verysatisfactory results and, if desired, super alkali No. 4 or otherprepared neutralizing agent in proportions varying from '75 pounds to225 pounds may be substituted for the caustic soda.

A small quantity of a wetting agent is added to the solution to causethe caustic alkali and soap to enter the pores of the metal neutralizingthe acid therein. This wetting agent may be one of the so-calledsoapless soaps and is used in proportions ranging from .02% to 5%.

For this purpose from to pounds of Orvus W. A. paste which is a sodiumsalt of the sulphated alcohol obtained from cocoanut oil, may be addedto the solution in the first washing tank. Wetting agents of this kindwill not form any insoluble lime soaps when used with hard water and areeffective in alkaline or acid media.

These wetting agents are used because of their high penetratingqualities very materially reducing the surface tension of the water soas to allow complete penetration of the pores of the metal by the alkaliand soap.

If it is desired to prevent foaming of the solution in this tank, thewetting agent may be also a foam eliminating agent such as sodiummetaphosphate or sodium hexametaphosphate. This may be obtainedcommercially under the name of Calgon and in use in this process 5 to 10gallons of this agent placed in the first washing tank give very goodresults. Other commercial products such as Tergitol may be used for thispurpose.

If it is found necessary or desirable to precipitate suspended orcolloidal particles in this solution a small amount, approximately .002%to .006% of a suitable chemical may be used.

Good results have been obtained by using 1 to 3 pounds of a mixture ofground. sulphate of aluminum, sodium carbonate and sodium bicarbonate,which mixture may be obtained commercially under the name of The OldSettler.

For the purpose of giving the steel a whiter color, small amounts of ableaching agent have been used in some instances. Sodium hypochloritemay be used in quantities of .01% to 04%; 1 to 2 gallons of thisbleaching agent in the first washing tank having given the metal awhiter color in actual use.

However, due to the fact that this bleachln agent is to some extent anoxidizing agent its use is not recommended where the steel is to be keptfor any length of time before cold rolling or other processing, andsince the bleachin agent is only used for giving a whiter color to thesteel and is not otherwise necessary in the present process, it may beeliminated without affecting the process.

Although the best results are obtained by using hot water as abovedescribed in the first washing tank, it should be understood that evenwith the use of cold water the above solution is very effective incleaning the pores and surfaces of the metal.

After the metal has been rinsed in the first washing tank it istransferred to the second washing tank which contains hot water, soap,caustic alkali, and a wetting agent and an ester, or one or both of itsresulting saponification products, which may be either a polyhydricalcohol or an ammonium soap, for the purpose of forming an imperviousfilm upon the surfaces of the metal.

Examples of esters which have produced a satisfactory coating upon themetal are diglycol laurate, diglycol oleate, glyceryl oleate andglyceryl monoricinoleate.

The water in this second washing tank may be maintained at a temperatureof 140 to 212 F. This tank contained about 4800 gallons and a smallamount of ordinary soap chips or soap powder, approximately .02% to.05%.

An amount ranging from 5 pounds to 15 pounds of Ozonite soap powder orchips in the second washing tank gave very satisfactory results.

Caustic alkali in amounts of from 131% to 135% were found sufficient inthis tank and in actual practice amounts of caustic soda varying from 15pounds to 30 pounds gave very satisfactory results.

The wetting agent used in this second tank may be any of the wettingagents above referred to as used in the first washing tank and may be inconcentrations of from .l% to 5%. In actual practice 5 to 20 pounds ofOrvus, as described above, has given very good results, and where a foameliminating agent is desired, 5 to 10 gallons of metaphosphate or sodiumhexametaphosphate may be substituted for the Orvus with verysatisfactory results.

Caustic alkali in the proportion of 275% to .55% may be used in thissecond washing tank and in actual practice 15 to 30 pounds of causticsoda has given very satisfactory results.

If desired, a small amount of bleaching agent such as sodiumhypochlorite, preferably about .025% to .05% may be added to thesolution, although as above stated in reference to the first washingtank, this blaching agent may be eliminated without afl'ecting theprocess.

For the purpose of providing an impervious film upon the surfaces of themetal to prevent formation of rust after the metal is thoroughlycleaned, an ester, a polyhydric alcohol, or ammonium soap, the twolatter being products of the saponification of the ester, may be addedto the solution in the second washing tank, about 25% to .625% beingsuflicient for the purpose.

Glycerine or glycerol, and glycol commonly called ethylene glycol areexamples of polyhydric alcohols which are suitable for this purpose, andammonium soap of a fatty acid such as lauric acid, oleic acid orlinoleic acid, namely, ammonium oleate, ammonium linoleate, and ammoniumlaurate are examples of soluble ammonium soaps which may be used to formthe impervious film upon the metal. From 10 to 25 gallons of glycerineor glycerol in the second washing tank have been found to be veryeffective.

If desired, a soluble ammonium soap such as ammonium oleate. ammoniumlincleate or ammonium laurate,- may be used in the second washing tanktogether with an ester of a polyhydric alcohol such as glycerol orglycol and a fatty ling acid before this protecting him is appliedthereto, the metal will remain entirely free from rust for aconsiderable length of time.

The ordinary soaps, wetting agents, esters, polyhydric alcohols orsoluble ammonium soaps all act as lubricants for the metal coils andmandrels when the process is used in a pickling machine of the type ofthe Greer patent above referred to, thus overcoming any effect thecaustic alkali might have upon the proper rotation of th mandrels andcoils.

It has been found that the protective quality of the polyhydric alcoholis enhanced by the presence of hydroxyl ions furnished by the causticalkali so that the glycerine or other polyhydric alcohols in combinationwith the alkali furnishes a better protective coat than either substancealone.

when the caustic alkali and polyhydric alcohol solution was used noblack scum appeared on the rolls of the cold rolling mills or on themetal itself as is the case where soluble oil is used as a protectivecoating upon the metal.

While the improved process has been described as carried out in theconventional manner by means of a pickling tank and two rinsing tanks,it should be understood that it is not the intention to limit theinvention to the use of two rinsing tanks, but, all of the ingredientsmay be contained in solution in one rinsing tank, or several rinsingtanks may be used each containing a solution of one or more of the abovenamed ingredients, and the following claims should be read with thisunderstanding.

I claim= l. The method of treating pickled metal directly after thepickling thereof to neutralize the adhering acid and inhibit rusting ofthe metal comprising rinsing it in a solution containing caustic alkali,a polyhydric alcohol taken from a group consisting of glycerine andglycol, and a wetting agent taken from a group consisting of sodiummetaphosphate and sodium hexametaphosphate.

2. The method of treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting oi the metalcomprising rinsing it in a solution containing caustic alkal, glycerine,and a wetting agent taken from a group consisting of sodiummetaphosphate and sodium hexametaphosphate.

3. The method of treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkal, apolyhydric alcohol taken from a group consisting of glycerine andglycol, ordinary soap, and a wetting agent taken from a group consistingof sodium metaphosphate and sodium hexametaphosphate.

4. The method of treating pickled metal comprising rinsing it in asolution containing caustic alkali, glycerine, ordinary soap, and awetting agent taken from a group consisting of sodium metaphosphate andsodium hexametaphosphate.

5. The method of treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkali, ordinarysoap, a precipitating agent consisting of a mixture of sulphate ofaluminum, sodium carbonate and sodium bicarbonate, a bleaching agent anda wetting agent taken -from a group consisting of sodium metaphosphateand sodium hexametaphosphate, and immersing the metal in a solutioncontaining a polyhydric alcohol taken from a group consisting ofglycerine and glycol.

6. The method of treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkali, ordinarysoap, a precipitating agent consisting of a mixture of sulphate ofaluminum, sodium carbonate and sodium bicarbonate, a bleaching agent anda wetting agent taken from a group consisting of sodium metaphosphateand sodium hexametaphosphate, and immersing the metal in a solutioncontaining glycerine.

'7. The method of treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkali, ordinarysoap, a precipitating agent consisting of a mixture of sulphate ofaluminum, sodium carbonate and sodium bicarbonate, a bleaching agent anda wetting agent taken from a group consisting of sodium metaphosphateand sodium hexametaphosphate, and immersing the metal in a solutioncontaining glycol.

8. The method of treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkali and awetting agent taken from the group consisting of sodium metaphosphateand sodium hexametaphosphate, and then coating the metal with a solutioncontaining a polyhydric alcohol taken from a groupconsisting ofglycerine and glycol.

9. The method of treating pickled metal directly after the picklingtherehf to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkali, ordinarysoap, and a wetting agent taken from the group consisting of sodiummetaphosphate and sodium hexametaphosphate, and then coating the metalwith a solution containing a polyhydric alcohol taken from a groupconsisting of glycerine and glycol.

10. The method of treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting or the metalcomprising rinsing it in a solution containing caustic alkali and awetting agent taken from the group consisting of sodium metaphosphateand sodium hexametaphosphate, and then'coating the metal with a solutioncontaining glycerine.

11. The method 01 treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkali, ordinarysoap, and a wetting agent taken irom the group consisting of sodiummetaphosphate and sodium hexametaphosphate, and then coating the metalwith a. solution containing glycerine.

12. The method of treating pickled metal directly after the picklingtheerof to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkali and thensubmerging the metal into a solution containing caustic alkali and apolyhydric alcohol taken from a group consisting of glycerine andglycol.

13. The method of treating pickled metal directly after the picklingthereof to neutralize the adhering acid and inhibit rusting of the metalcomprising rinsing it in a solution containing caustic alkali and thensubmerging the metal into a hot solution containing caustic alkali and apolyhydric alcohol taken from a group consisting of glycerine and glycoland then removing the hot metal from the hot solution and permitting thewater to quickly evaporate from the surface thereof leaving animpervious film of the polyhydric alcohol thereon.

ROBERT W. SHOEMAKER.

